Polishing slurry and polishing method using same

ABSTRACT

Polishing slurry is caused to be present between a surface of a soft magnetic layer and a polishing tool such as a polishing pad and the surface of the soft magnetic layer and the polishing tool are moved relative to each other. The polishing slurry contains silica particles as abrading particles, compounds containing carboxylic acid and amino polycarboxylic acid and an oxidizing agent as a polishing accelerator, organic and/or inorganic compound of phosphoric acid, nitride and/or nitrite as an anti-corrosion agent and a pH conditioner such that the slurry has pH value between 4 and 11.

This application claims priority on Japanese Patent Application2006-256756 filed Sep. 22, 2006.

BACKGROUND OF THE INVENTION

This invention relates to polishing slurry for and a method of polishingthe surface of a soft magnetic layer formed on the surface of asubstrate for a perpendicular magnetic recording hard disk.

Data processing devices for recording and reproducing data such ascharacters, images and sounds are coming to be incorporated not onlyinto a personal computer but also into an electronic apparatus such as atelevision, a camera, a portable music player and a portable telephone.Such data processing devices are required to have a higher processingcapability (or an increased recording capacity) and an improved accuracyin reproduction, as well as compactness.

Data processing devices record and reproduce such data magnetically bymeans of a magnetic head on and from a magnetic recording medium. Asmagnetic recording media of this kind, perpendicular magnetic recordingdisks are coming to be investigated, as disclosed, for example, inJapanese Patent Publications Tokkai 2004-362746, 5-266455 and 6-103554.

Perpendicular magnetic recording disks are formed by forming a softmagnetic layer for improving the efficiency of recording andreproduction of data signals and a perpendicular magnetic recordinglayer comprising a perpendicular magnetization film for recording datasignals by a conventionally known thin-film technology such assputtering. In addition to these layers, a non-magnetic layer havingfunctions of improving the crystalline characteristics of theperpendicular magnetic recording layer and controlling the crystallineparticle diameters is formed. In order to prevent the generation ofnoise caused by the displacement of a magnetic wall due to a leakedmagnetic field (or spike noise, in particular), the soft magnetic layermay be divided into two layers for inserting a hard magnetic layer inbetween and pinning the magnetic wall so as to inhibit the movement ofthe magnetic wall, as disclosed in Japanese Patent Publication Tokkai5-266455. In order to make the reproduced output waveform uniform withinthe surface of the perpendicular magnetic recording disk, or forimproving the modulation characteristics (or the uniformity of thereproduced output waveform for one cycle of the recording medium at thetime of reproduction), furthermore, it has been known to formapproximately concentric circular texturing marks in the circumferentialdirection on the surface of the non-magnetic substrate by carrying out atexturing process, to thereafter form a soft magnetic layer through ahard magnetic layer (also referred to as the bias layer) on the surfaceof this non-magnetic substrate, and to form a perpendicular magneticrecording layer thereon, as disclosed in Japanese Patent PublicationTokkai 6-103554.

In summary, a perpendicular magnetic recording layer for recording datais formed above a soft magnetic layer (also referred to as a softmagnetic backing layer) which can pass the magnetic fluxes from themagnetic head easily. With such a two-layer structure, the intensity ofthe generated magnetic field from the magnetic head and the slope of themagnetic field are increased so as to improve the resolution ofrecordation, and the leaked magnetic fluxes from the medium is alsoincreased such that a high-density recording becomes possible.

As the material for the soft magnetic layer, NiFe alloys and amorphousalloys with Co as the principal component are generally used but a filmthickness of 0.1 μm-several μm is necessary in order to obtain asufficient recording-reproduction characteristics with such a material.From the point of view of mass production, the production cost would betoo high if soft magnetic layers with such thickness were to be producedby sputtering. For this reason, soft magnetic layers with Fe, Co, B,etc. being added to NiP such as Ni—Fe—P layers and Ni—Co—P layers andthose comprising soft magnetic NiP with concentration of P less than 6%are being used to form films by an electroless plating method in orderto reduce the cost of mass production, as disclosed, for example, inJapanese Patent Publications Tokkai 2004-335068, 2005-353177, 2006-21259and 2006-63438.

Such soft magnetic layers, like soft magnetic NiP layers withconcentration of P less than 12% or more, must have the layer surfaceflattened by polishing. Since NiP layers with P concentration 12% ormore have a high acid resistance, a strongly acidic polishing liquidwith a high etching power is used but soft magnetic layers as describedabove are low in acid resistance. If a strongly acidic polishing liquidis used for polishing their surfaces, the layer surface is unevenlydissolved and cannot be made flat and even. Moreover, nickel phosphateis recrystallized due to corrosion and a black film is formed.

For this reason, alkaline polishing liquids with pH8 or high were usedor the size of the abrading particles in the polishing slurry wasspecified for the surface polishing of a soft magnetic layer, asdisclosed in Japanese Patent Publications Tokkai 2004-259378,2004-342294, 2005-149603, 2005-216465 and 2005-302137.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide polishing slurrycapable of polishing the surface of a soft magnetic layer formed on thesurface of a substrate for a perpendicular magnetic recording hard diskwithout corroding it excessively and at a high polishing rate at a highlevel of accuracy, as well as a polishing method using such polishingslurry.

Polishing slurry of this invention is characterized as comprisingabrading particles, a polishing accelerator, an anti-corrosion agent, apH conditioner and water.

Silica particles are contained as the abrading particles. They arecolloidal silica with an average particle diameter of 20 nm or more and100 nm or less.

A compound containing carboxylic acid, a compound containing aminopolycarboxylic acid and an oxidizing agent are contained as thepolishing accelerator. At least one of the compound containingcarboxylic acid and the compound containing amino polycarboxylic acid isammonium salt. The oxidizing agent is hydrogen peroxide water.

The anti-corrosion agent includes one or more compounds selected fromthe group consisting of organic and inorganic compounds of phosphoricacid, nitrides and nitrites.

The pH conditioner is added such that the polishing slurry isconditioned to be between pH4 and pH11.

If the pH value of the polishing slurry is less than 7, theanti-corrosion agent comprises an organic or inorganic compound ofphosphoric acid and the pH conditioner comprises hydroxylic acids.

If the pH value of the polishing slurry is more than 7, theanti-corrosion agent comprises a nitride and the pH conditionercomprises an amine.

With respect to the total weight of the polishing slurry of thisinvention, silica particles are contained at a rate of 1 weight % ormore and 30 weight % or less, the compound containing carboxylic acidand the compound containing amino polycarboxylic acid of the polishingaccelerator are together contained at a rate of 0.01 weight % or moreand 20 weight % or less, the oxidizing agent of the polishingaccelerator is contained at a rate of 0.1 weight % or more and 20 weight% or less, and the anti-corrosion agent is contained at a rate of 0.001weight % or more and 5 weight % or less.

A method of this invention for polishing the surface of a soft magneticlayer formed on the surface of a substrate for a perpendicular magneticrecording hard disk is characterized as comprising the steps of causingpolishing slurry of this invention as described above to be presentbetween the surface of the soft magnetic layer and a polishing toolwhich preferably comprises a polishing pad, and causing the surface ofthe soft magnetic layer and the polishing tool to move relative to eachother;

According to this invention, the surface of a soft magnetic layer formedon the surface of a substrate for a perpendicular magnetic recordinghard disk can be made flat and even (such that the average surfaceroughness (Ra) is 0.2 nm or less and the surface waviness is 0.1 nm orless) at a high polishing rate and with a high level of accuracy,without excessively corroding the surface of the soft magnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B respectively show a lower lapping plate and an upperlapping plate of a polishing machine that may be used for the method ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION

Polishing slurry of this invention is for polishing the surface of asoft magnetic layer formed on the surface of a substrate for aperpendicular magnetic recording hard disk, comprising abradingparticles, a polishing accelerator, an anti-corrosion agent, an pHconditioner and water.

As the abrading particles, silica particles are included, and theiraverage diameter is in the range of 5 nm or more and 300 nm or less. Assilica particles, colloidal silica obtainable by hydrolysis such asmetallic alkoxides and sodium silicate or fumed silica obtainable by thespray-dry method, etc. may be used. It is preferable to use colloidalsilica with average diameter in the range of 20 nm or more and 100 nm orless.

Examples of polishing accelerator include compounds containingcarboxylic acid, compounds containing amino polycarboxylic acid andoxidizing agents.

Examples of compound containing carboxylic acid include compounds ofcarboxylic acid and polyvalent carboxylic acid such as oxalic acid,lactic acid, malic acid, citric acid, malonic acid, tartaric acid,succinic acid, fumaric acid, maleic acid, formic acid, acetic acid,butyric acid, valerianic acid, phthalic acid, isophthalic acid,terephthalic acid, salicylic acid and oxocarboxylic acid. A preferredexample of compound containing carboxylic acid is ammonium oxalate.

Examples of compound containing amino polycarboxylic acid includecompounds such as ethylene diamine-4-acetic acid, diethylenetriamine-5-acetic acid, hydroxy ethylene diamine-2-acetic acid,triethylene tetramine-6-acetic acid, hydroxy ethylimino-2-acetic acid,dihydroxy ethylglycine and 1,3-propane diamine-4-acetic acid. Beingcapable of exhibiting similar effects as these compounds, aminopolyphosphonic acid may be also included. A preferred example ofcompound containing amino polycarboxylic acid is diethylenetriamine-5-acetic acid-2-ammonium.

Between compounds containing carboxylic acid and compounds containingamino polycarboxylic acid, a compound of either category is an ammoniumsalt.

Examples of oxidizing agent contained in a polishing accelerator includehydrogen peroxide water, ozone water, sodium hypochlorite, potassiumhypochlorite and calcium hypochlorite. A preferred example of oxidizingagent is hydrogen peroxide water.

Examples of anti-corrosion agent include compounds having one or moreselected from organic compounds of phosphoric acid, inorganic compoundsof phosphoric acid, nitrides and nitrites.

Examples of organic and inorganic salts of phosphoric acid includecompounds of phosphoric acid, polyphosphoric acid, pyrophosphoric acid,metaphosphoric acid and phosphonic acid. Examples of nitride includetriazoles such as benzotriazole, triazole, imitazole and tolyltrizoleand imidazoles. Examples of nitrite include nitrites such as sodiumnitrite, potassium nitrite, calcium nitrite, ethyl nitrite, isoamylnitrite, isobutyl nitrite and isopropyl nitrite, and nitrite esters.

When the acidity-alkalinity of the polishing slurry of this invention isadjusted to pH7 or over, inorganic phosphoric acids are preferable asthe anti-corrosion agent. When the acidity-alkalinity of the polishingslurry of this invention is adjusted to less than pH7, nitrides arepreferable as the anti-corrosion agent.

Examples of pH conditioner include salts of phosphoric acid and boricacid such as phosphoric acid-2-hydrogen-ammonium, phosphoricacid-hydrogen-2-ammonium and ammonium tetraborate tetrahydrate.

When the acidity-alkalinity of the polishing slurry of this invention isadjusted to pH7 or over, alkaline pH conditioners are preferred such asammonia water, ammonium carbonate, and amines such as ethylamine,methylamine, triethyl amine and tetramethyl amine. Salts of phosphoricacid are included as preferred example of pH conditioner.

When the acidity-alkalinity of the polishing slurry of this invention isadjusted to less than pH7, acidic pH conditioners are preferred,inclusive of hydroxylic acids such as lactic acid, citric acid, malicacid, tartaric acid and glyceric acid.

A method of this invention for polishing the surface of a soft magneticlayer formed on the surface of a substrate for a perpendicular magneticrecording hard disk includes the steps of causing polishing slurry ofthis invention as described above to be present between the surface ofthe soft magnetic layer of the substrate and a polishing tool and movingthe surface of the soft magnetic layer and the polishing tool relativeto each other. Preferable examples of the polishing tool includepolishing pads.

As a preferable example, a double-surface polishing machine as shown inFIGS. 1A and 1B may be used to polish the surfaces of soft magneticlayers formed on the surfaces of a substrate 15 for a perpendicularmagnetic recording hard disk to make them flat and even. As shown, thepolishing of the both surfaces of the substrate 15 is carried out byplacing the substrate 15 at the opening 14 of a solar gear 17 of a lowerlapping plate 12 having a polishing pad 10 pasted on its surface and aplanet gear 13 engaging with an internal gear 16, pressing it from abovewith an upper lapping plate 11 having another polishing pad 10′ on itssurface, and causing the solar gear 17 to rotate in the direction ofarrow W by means of an external driver motor while supplying polishingslurry of this invention through openings 18 in the upper lapping plate11 into the space between the upper and lower lapping plates 11 and 12such that the planet gear 13 rotates in the direction of arrow X andaround the solar gear in the direction of arrow Y.

Prior art sheets of suede, woven or unwoven cloth, flocked cloth orfoamed material may be cut into the form of a pad may be used as thepolishing pads 10 and 10′. Polishing pads of a suede type are preferablyused.

Polishing Test 1

Samples of polishing slurry Test Examples (1-1)-(1-12) and ComparisonExamples (1-1)-(1-5) (all acidic with pH value less than 7 except forComparison Example (1-5)) were used to polish both surfaces ofsubstrates for a perpendicular magnetic recording hard disk having softmagnetic layers formed on the surfaces and the results were compared interms of polishing rate, average surface roughness (Ra), surfacewaviness, numbers of corrosion, scratches and particles after thepolishing.

The substrates that were polished were aluminum substrates with diameter95 mm having non-magnetic Ni—P films (with P concentration of 12% ormore) formed on both surfaces by the electroless plating method andNi—Co—P layers (soft magnetic layers) with thickness about 3.0 μm formedthereon. The average surface roughness (Ra) (average surface roughnessof their soft magnetic layers) of these substrates before the polishingwas 0.50 nm-0.10 nm, and their surface waviness (Wa) was 0.10 nm-0.15nm.

FIGS. 1A and 1B show the double-surface polishing machine (product name:9BF, produced by Hamai Sangyo Kabushiki Kaisha) that was used for thepolishing. Polishing pads of the suede-type were pasted onto the upperand lower lapping plates, and both surfaces of ten substrates werepolished simultaneously. The conditions of the polishing were as shownin Table 1.

TABLE 1 Polishing pressure 90 gf/cm² Rotational speed Upper lappingplate 40 rpm of lapping plates Lower lapping plate 40 rpm Supply rate ofpolishing slurry 200 ml/minute Polishing time 10 minutes

The polishing rate, defined as the polished quantity per unit time inunits of mg/minute), is obtained by dividing the difference in weight ofthe substrate before and after the polishing by the polishing time. Theweight of the substrate was measured by using a commercially availablemeasuring instrument (product name: HF-20 produced by A&M Corporation).

The average surface roughness (Ra) was measured in units of nm by usingan atomic force microscope AFM (product name: Nanoscope Dimension 3100Series produced by Digital Instruments Corporation) over a measurementfield of vision of 10 μm×10 μm.

The surface waviness (Wa) was measured in units of nm by using anon-contact three-dimensional surface profiler (product name: NewView5000 produced by ZYGO CORPORATION) (object lens=10 times; intermediatelens=0.8; and cutoff filter=0.05 mm-0.5 mm).

The numbers of corrosion, scratches and particles per surface were eachcounted from each of the surfaces of the substrate after the polishingby using a disk surface observation device (Product Name: MicroMaXVMX-2100, produced by Vision Sitec, Ltd.) and averaging the countednumbers.

The composition of each of the samples of polishing slurry Test Examples(1-1)-(1-12) is shown in Tables 2 and 3 (in units of weight %). TestExample (1-1) is a preferred example in the range of pH4-pH5. TestExample (1-2) is different therefrom only in that salt of phosphoricacid is not added. Test Example (1-3) is a preferred example in therange of pH5-pH6. Test Example (1-4) is a preferred example in the rangeof less than and about equal to pH7. Test Example (1-5) is differentfrom Test Example (1-4) only in that the average diameter of the silicaparticles is 80 nm. Test Example (1-6) has nitrous acid added asanti-corrosion agent. Test Example (1-7) has a nitrite (benzotriazole)added as anti-corrosion agent. Test Example (1-8) has a reduced amount(concentration) of amino polycarboxylic acid. Test Example (1-9) has anincreased concentration (quantity) of oxidizing agent (hydrogen peroxidewater). Test Example (1-10) has an increased concentration (quantity) ofcompound of carboxylic acid (ammonium oxalate). Test Example (1-11) usespotassium oxalate as compound of carboxylic acid. Test Example (1-12)uses ammonium formate as compound of carboxylic acid.

The composition of each of the samples of polishing slurry ComparisonExamples (1-1)-(1-5) is shown in Table 4 (in units of weight %).Comparison Example (1-1) is conditioned to pH3.5. Comparison Example(1-2) does not include any anti-corrosion agent and is conditioned topH4.5. Comparison Example (1-3) is conditioned to less than pH3.Comparison Example (1-4) is conditioned to pH4.6. Comparison Example(1-5) is conditioned to be alkaline at pH9.3.

TABLE 2 Test Examples 1-1 1-2 1-3 1-4 1-5 1-6 Silica particles 40 nm 5.05.0 5.0 5.0 — 5.0 80 nm — — — — 5.0 — Compound of Ammonium oxalate  0.25 0.25  0.25  0.25  0.25  0.25 carboxylic acid Potassium oxalate — — — —— — Ammonium formate — — — — — — Compound of amino DTPA 2 ammonium 5.05.0 5.0 5.0 5.0 5.0 polycarboxylic acid Oxidizing agent Hydrogenperoxide 2.5 2.5 2.5 2.5 2.5 2.5 water Anti-corrosion agent Inorganicsalt of 0.5 0.5 0.5 0.5 0.5 — phosphoric acid Nitrite — — — — — 0.5Benzotriazole — — — — — — pH conditioner Ammonia water — — — 0.1 0.1 0.1Lactic acid 0.2 0.2 — — — — Salt of phosphoric acid 0.2 — 0.2 0.2 0.20.2 Water Pure water 86.35 86.55 86.55 86.45 86.45 86.45 pH 4.6 4.5 5.56.7 6.0 4.3 DTPA: Diethylene triamine-5-acetic acid

TABLE 3 Test Examples 1-7 1-8 1-9 1-10 1-11 1-12 Silica particles 40 nm5.0 5.0 5.0 5.0 5.0 5.0 80 nm — — — — — — Compound of Ammonium oxalate 0.25  0.25  0.25  0.50 — — carboxylic acid Potassium oxalate — — — — 0.25 — Ammonium formate — — — — —  0.25 Compound of amino DTPA 2ammonium 5.0 2.5 5.0 5.0 5.0 5.0 polycarboxylic acid Oxidizing agentHydrogen peroxide 2.5 2.5 5.0 2.5 2.5 2.5 water Anti-corrosion agentInorganic salt of — 0.5 0.5 0.5 0.5 0.5 phosphoric acid Nitrite — — — —— — Benzotriazole 0.1 — — — — — pH conditioner Ammonia water — — — — — —Lactic acid 0.2 — — — — — Salt of phosphoric acid 0.2 0.2 0.2 0.2 0.20.2 Water Pure water 86.75 89.05 84.04 86.30 86.55 86.55 pH 4.1 5.8 5.56.0 5.6 5.0 DTPA: Diethylene triamine-5-acetic acid

TABLE 4 Comparison Examples 1-1 1-2 1-3 1-4 1-5 Silica particles 40 nm5.0 5.0 5.0 5.0 5.0 Compound of Ammonium oxalate  0.25  0.25  0.25 — —carboxylic acid Potassium oxalate — — —  0.25  0.25 Compound of aminoDTPA 2 ammonium 5.0 5.0 5.0 — — polycarboxylic acid DTPA 5 sodium — — —5.0 5.0 Oxidizing agent Hydrogen peroxide water 2.5 2.5 2.5 2.5 2.5Anti-corrosion agent Inorganic salt of phosphoric acid 0.5 — 0.5 0.5 —pH conditioner Lactic acid 0.3 0.1 1.0 0.5 — Salt of phosphoric acid 0.20.2 0.2 0.2 — Water Pure water 86.25 86.95 85.55 86.05 87.25 pH 3.5 4.52.9 4.6 9.3 DTPA: Diethylene triamine-5-acetic acid

Test results with Test Examples (1-1)-(1-12) and Comparison Examples(1-1)-(1-5) are summarized in Tables 5 and 6. Regarding the numbers ofcorrosion, scratches and particles, A indicates less than 10, Bindicates 10 or more and less than 20, C indicates 20 or more and lessthan 40, and D indicates 40 or more.

TABLE 5 Test Examples 1-1 1-2 1-3 1-4 1-5 1-6 Polishing rate (mg/minute)6.8  6.2  6.0  4.3  6.4  4.9  Average surface 0.14 0.14 0.11 0.10 0.190.15 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.07 0.08 0.06 0.060.09 0.07 Corrosion (number/surface) B B A A B B Scratches(number/surface) B B B B B B Particles (number/surface) B B B B B B TestExamples 1-7 1-8 1-9 1-10 1-11 1-12 Polishing rate (mg/minute) 5.0  5.5 5.9  5.4  5.0  4.4  Average surface 0.13 0.12 0.13 0.11 0.16 0.18roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.07 0.07 0.06 0.07 0.080.09 Corrosion (number/surface) B B A A B B Scratches (number/surface) BB B B B B Particles (number/surface) B B B B B B

TABLE 6 Comparison Examples 1-1 1-2 1-3 1-4 1-5 Polishing rate(mg/minute) 7.0  7.2  7.7  4.0  2.0  Average surface 0.25 0.24 0.25 0.200.11 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.12 0.11 0.10 0.080.09 Corrosion (number/surface) D D D C B Scratches (number/surface) C CC B B Particles (number/surface) B B B B B

Tables 5 and 6 show that a high level of accuracy in polishing isaccomplished with each of the Test Examples embodying this inventionwith average surface roughness of 0.2 nm or less and surface waviness of0.1 nm or less and that equivalent or better results are obtainedregarding corrosion, scratches and particles compared to any ofComparison Examples.

Although equivalent results are obtained with Comparison Example (1-5),this slurry is alkaline and its polishing rate is lower (less than ½).

Polishing Test 1 was for the polishing of a Ni—Co—P layer (soft magneticlayer) and the results depend on the material of the soft magneticlayer. In the case of a Ni—Co—P layer, however, it can be understoodfrom the results of Comparison Examples (1-1) and (1-3) that corrosionsoccur even if an anti-corrosion agent is added if the polishing slurryhas pH4 or less in the case of a Ni—Co—P layer.

Results of Comparison Examples (1-1) and (1-2) indicate that corrosionsoccur unless an anti-corrosion agent is added if the polishing slurryhas pH4 or over and is weakly acid with pH7 or lower. In other words, inthe case of a Ni—Co—P layer, it is necessary that acidity of thepolishing slurry be over pH4 and pH7 or below and an anti-corrosionagent be added.

From the results of Comparison Examples (1-4) and (1-5), as compared tothe results of Comparison Examples (1-1)-(1-3), it is understood thatthe polishing rate drops significantly if ammonium salt is not containedas polishing accelerator. It is to be noted that every example accordingto this invention contains ammonium salt.

Polishing Test 2

Samples of polishing slurry Test Examples (2-1)-(2-11) and ComparisonExamples (2-1)-(2-6) (all alkaline with pH value 8 or more) were used topolish both surfaces of substrates for a perpendicular magneticrecording hard disk having soft magnetic layers formed on the surfacesand the results were compared in terms of polishing rate, averagesurface roughness (Ra), surface waviness, numbers of corrosion,scratches and particles after the polishing.

The substrates that were polished were similar to those used inPolishing Test 1 with diameter 95 mm having non-magnetic Ni—P films(with P concentration 12% or more) formed on both surfaces by theelectroless plating method and Ni—Co—P layers (soft magnetic layers)with thickness about 3.0 μm formed thereon. The average surfaceroughness (Ra) (average surface roughness of their soft magnetic layers)of these substrates before the polishing was 0.50 nm-0.10 nm, and theirsurface waviness (Wa) was 0.10 nm-0.15 nm.

A double-surface polishing machine (product name: 9BF, produced by HamaiSangyo Kabushiki Kaisha), as used in Polishing Test 1 and describedabove, was used for the polishing. Polishing pads of the suede-type werepasted onto the upper and lower lapping plates, and both surfaces of tensubstrates were polished simultaneously. The conditions of the polishingwere as shown in Table 1 described above.

The polishing rate, the average surface roughness (Ra) and the surfacewaviness (Wa) were measured as described above.

The numbers of corrosion, scratches and particles per surface were eachcounted also as described above and the counted numbers were averaged.

The composition of each of the samples of polishing slurry Test Examples(2-1)-(2-11) is shown in Tables 7 and 8. Test Example (2-1) is apreferred example with alkalinity in the neighborhood of pH9. TestExample (2-2) is different therefrom only in that anti-corrosive agentis not added. Test Example (2-3) is different from Test Example (2-1) inthat inorganic salt of phosphoric acid is added as anti-corrosion agent.Test Example (2-4) has ammonium carbonate added as pH conditioner. TestExample (2-5) has tetramethyl ammonium hydroxide added as pHconditioner. Test Example (2-6) has salt of boric acid added as pHconditioner. Test Example (2-7) is an example not using any pHconditioner. Test Example (2-8) has phthalic acid added as polishingaccelerator. Test Example (2-9) has tartaric acid added as polishingaccelerator. Test Example (2-10) has boric acid added as polishingaccelerator. Test Example (2-11) has malonic acid added as polishingaccelerator.

TABLE 7 Test Examples 2-1 2-2 2-3 2-4 2-5 2-6 Silica particles 40 nm 5.05.0 5.0 5.0 5.0 5.0 Compound of Ammonium oxalate  0.25  0.25  0.25  0.25 0.25  0.25 carboxylic acid Phthalic acid — — — — — — Tartaric acid — —— — — — Boric acid — — — — — — Malonic acid — — — — — — Compound ofamino DTPA 2 ammonium 5.0 5.0 5.0 5.0 5.0 5.0 polycarboxylic acidOxidizing agent Hydrogen peroxide 2.5 2.5 2.5 2.5 2.5 2.5 waterAnti-corrosion agent Inorganic salt of — — 0.5 — — — phosphoric acidBenzotriazole 0.1 — — 0.1 0.1 0.1 pH conditioner Ammonia water 0.5 0.50.4 — — 0.5 Ammonium carbonate — — — 0.5 — — Tetramethyl — — — — 0.5 —ammonium hydroxide Phosphoric acid 0.2 0.2 0.2 0.2 0.2 — Boric acid (pH— — — — — 0.2 conditioner) Water Pure water 86.45 86.55 86.15 86.4586.45 86.95 pH 8.8 8.8 8.8 8.2 8.3 8.4 DTPA: Diethylenetriamine-5-acetic acid

TABLE 8 Test Examples 2-7 2-8 2-9 2-10 2-11 Silica particles 40 nm 5.05.0 5.0 5.0 5.0 Compound of carboxylic acid Ammonium oxalate  0.25 — — —— Phthalic acid —  0.25 — — — Tartaric acid — —  0.25 — — Boric acid — ——  0.25 — Malonic acid — — — —  0.25 Compound of amino DTPA 2 ammonium5.0 5.0 5.0 5.0 5.0 polycarboxylic acid Oxidizing agent Hydrogenperoxide 2.5 2.5 2.5 2.5 2.5 water Anti-corrosion agent Inorganic saltof — — — — — phosphoric acid Benzotriazole 0.1 0.1 0.1 0.1 0.1 pHconditioner Ammonia water 0.2 1.6 1.2 1.1 1.7 Ammonium carbonate — — — —— Tetramethyl — — — — — ammonium hydroxide Phosphoric acid — 0.2 0.2 0.20.2 Boric acid (pH — — — — — conditioner) Water Pure water 86.95 85.1585.50 85.60 85.00 pH 7.1 8.8 8.8 8.8 8.8 DTPA: Diethylenetriamine-5-acetic acid

The composition of each of the samples of polishing slurry ComparisonExamples (2-1)-(2-6) is shown is Table 9 (in units of weight %).Comparison Example (2-1) is conditioned to above pH11. ComparisonExample (2-2) has EDTA-4-Na added as polishing accelerator. ComparisonExample (2-3) has HEDP-4-Na added as polishing accelerator. ComparisonExample (2-4) has DTPA-5-Na added as polishing accelerator. ComparisonExample (2-5) has caustic soda added as pH conditioner. ComparisonExample (2-6) has no pH conditioner added but alkylene glycol andglycerol added.

TABLE 9 Comparison Examples 2-1 2-2 2-3 2-4 2-5 2-6 Silica particles 40nm 5.0 5.0 5.0 5.0 5.0 5.0 Compound of Ammonium oxalate  0.25  0.25 0.25  0.25  0.25  0.25 carboxylic acid Carboxylic acid — — — — — 1.2derivative Compound of amino DTPA-2-ammonium 5.0 — — — 5.0 —polycarboxylic acid EDTA-4-Na — 5.0 — — — 7.0 HEDP-4-Na — — 5.0 — — —DTPA-5-Na — — — 5.0 — — Oxidizing agent Hydrogen peroxide 2.5 2.5 2.52.5 2.5 — water Anti-corrosion agent Benzotriazole 0.1 0.1 0.1 0.1 0.1 —pH conditioner Ammonia water 10.0  — — — — — Caustic soda — — — —  0.05— Salt of phosphoric acid — 0.2 0.2 0.2 — — Others Alkylene glycol — — —— —  0.24 glycerol — — — — — 0.1 Water Pure water 77.15 86.95 86.9586.95 87.10 92.51 pH 11.1  9.0 9.0 8.4 11.0  9.0 DTPA: Diethylenetriamine-5-acetic acid Carboxylic acid derivative: Polycarboxylatepolymer type surfactant (product name: DEMOL-EP produced by KaoKabushiki Kaisha) Alkylene glycol: diethylene glycol mono-n-butyletherEDTA: Ethylene diamine-4-acetic acid HEDP: Hydroxy ethylene diphosphonicacid (compound of amino polyphosphonic acid) having effects similar toamino polycarboxylic acids.

Test results with Test Examples (2-1)-(2-11) and Comparison Examples(2-1)-(2-6) are summarized in Tables 10 and 11. Regarding the numbers ofcorrosion, scratches and particles, A indicates less than 10, Bindicates 10 or more and less than 20, C indicates 20 or more and lessthan 40, and D indicates 40 or more, as in Tables 4 and 5.

TABLE 10 Test Examples 2-1 2-2 2-3 2-4 2-5 2-6 Polishing rate(mg/minute) 3.5  3.1  2.4  3.9  3.8  2.8  Average surface 0.11 0.11 0.110.12 0.10 0.12 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.06 0.060.06 0.07 0.06 0.06 Corrosion (number/surface) A B A A A A Scratches(number/surface) B B B B B B Particles (number/surface) B B B B B B TestExamples 2-7 2-8 2-9 2-10 2-11 Polishing rate (mg/minute) 3.4  3.0  2.8 2.7  2.7  Average surface roughness (Ra) (nm) 0.11 0.10 0.10 0.12 0.10Surface waviness (Wa) (nm) 0.06 0.07 0.06 0.08 0.06 Corrosion(number/surface) A A A A A Scratches (number/surface) B B B B BParticles (number/surface) B B B B B

TABLE 11 Comparison Examples 2-1 2-2 2-3 2-4 2-5 2-6 Polishing rate(mg/minute) 6.4 2.4 1.8 2.5 2.6 1.6 Average surface 0.28 0.11 0.11 0.100.11 0.10 roughness (Ra) (nm) Surface waviness (Wa) (nm) 0.12 0.06 0.070.06 0.06 0.06 Corrosion (number/surface) D A A A A A Scratches(number/surface) C B B B B A Particles (number/surface) B B B B B A

Tables 10 and 11 show that a high level of accuracy in polishing isaccomplished with each of the Test Examples embodying this inventionwith average surface roughness of 0.2 nm or less and surface waviness of0.1 nm or less and that equivalent or better results are obtainedregarding corrosion, scratches and particles compared to any ofComparison Examples.

Although equivalent results are obtained with Comparison Example (2-6),this slurry sample does not contain any pH conditioner and its polishingrate is lower (less than ½) than by any of the other ComparisonExamples.

Polishing Test 2 was for the polishing of a Ni—Co—P layer (soft magneticlayer) and the results depend on the material of the soft magneticlayer. In the case of a Ni—Co—P layer, however, it can be understoodfrom the results of Comparison Examples (2-1) and (2-5) that corrosiontakes place even if an anti-corrosion agent is added if the polishingslurry exceeds pH 11. In other words, in the case of a Ni—Co—P layer, itis understood that the pH value should be 11 or less.

Results of Test Examples (2-1)-(2-11) containing ammonium salts of DTPAas amino polycarboxylic acid compound and Comparison Examples(2-2)-(2-4) containing sodium salts of EDTA, HEDP and DTPA indicate thatsamples containing ammonium salts as amino polycarboxylic acid compoundof polishing accelerator has equivalent or higher polishing ratescompared to those containing sodium salts. From Comparison Examples(2-1) and (2-5), furthermore, it can be learned that the polishing rateincreases if ammonia water (amine) is added as pH conditioner than ifcaustic soda is added.

1. Polishing slurry for polishing the surface of a soft magnetic layerformed on the surface of a substrate for a perpendicular magneticrecording hard disk, said polishing slurry comprising: abradingparticles; a polishing accelerator; an anti-corrosion agent; a pHconditioner; and water; wherein said abrading particles include silicaparticles; wherein said polishing accelerator includes a compoundcontaining carboxylic acid, a compound containing amino polycarboxylicacid and an oxidizing agent; wherein said anti-corrosion agent includesone or more compounds selected from the group consisting of organic andinorganic compounds of phosphoric acid, nitrides and nitrites; andwherein said polishing slurry is conditioned to be between pH4 and pH 11by said pH conditioner.
 2. The polishing slurry of claim 1 wherein atleast either of said compound containing carboxylic acid and saidcompound containing amino polycarboxylic acid is ammonium salt.
 3. Thepolishing slurry of claim 1 wherein said oxidizing agent is hydrogenperoxide water.
 4. The polishing slurry of claim 1 wherein the pH valueof said polishing slurry is less than 7 and said anti-corrosion agentcomprises an organic or inorganic compound of phosphoric acid.
 5. Thepolishing slurry of claim 1 wherein the pH value of said polishingslurry is more than 7 and said anti-corrosion agent comprises a nitride.6. The polishing slurry of claim 1 wherein the pH value of saidpolishing slurry is less than 7 and said pH conditioner compriseshydroxylic acids.
 7. The polishing slurry of claim 1 wherein the pHvalue of said polishing slurry is more than 7 and said pH conditionercomprises an amine.
 8. The polishing slurry of claim 1 wherein saidsilica particles comprise colloidal silica with an average particlediameter of 5 nm or more and 300 nm or less.
 9. The polishing slurry ofclaim 1 wherein said silica particles comprise colloidal silica with anaverage particle diameter of 20 nm or more and 100 nm or less.
 10. Thepolishing slurry of claim 1 wherein said silica particles are containedat a rate of 1 weight % or more and 30 weight % or less of the totalweight of said polishing slurry; wherein said compound containingcarboxylic acid and said compound containing amino polycarboxylic acidare together contained at a rate of 0.01 weight % or more and 20 weight% or less of the total weight of said polishing slurry; wherein saidoxidizing agent is contained at a rate of 0.1 weight % or more and 20weight % or less of the total weight of said polishing slurry; andwherein said anti-corrosion agent is contained at a rate of 0.001 weight% or more and 5 weight % or less of the total weight of said polishingslurry.
 11. A method of polishing the surface of a soft magnetic layerformed on the surface of a substrate for a perpendicular magneticrecording hard disk; said method comprising the steps of: causingpolishing slurry to be present between said surface of said softmagnetic layer and a polishing tool; and causing said surface of saidsoft magnetic layer and said polishing tool to move relative to eachother; wherein said polishing slurry comprises: abrading particles; apolishing accelerator; an anti-corrosion agent; a pH conditioner; andwater; wherein said abrading particles include silica particles; whereinsaid polishing accelerator includes a compound containing carboxylicacid, a compound containing amino polycarboxylic acid and an oxidizingagent; wherein said anti-corrosion agent includes one or more compoundsselected from the group consisting of organic and inorganic compounds ofphosphoric acid, nitrides and nitrites; and wherein said polishingslurry is conditioned to be between pH4 and pH11 by said pH conditioner.12. The method of claim 11 wherein said polishing tool comprises apolishing pad.